Why have Miró's yellows lost their shine?

Closely associated with the history of surrealism, Joan Miró (1893-1983) is famous for his works featuring bright colors and dreamlike shapes. One of the colors he used in the 1970s, however, has deteriorated over time, becoming dull and powdery: it is cadmium yellow. A study published in July in the journal Heritage Science attributes the degradation of Miró’s works, as well as those of Picasso and Matisse, to a specific brand of painting: Lucien Lefebvre-Foinet.

Marketed in the 1870s, cadmium yellow is a pigment obtained from cadmium and sulfur. In Miró’s workshops, there are several tubes of cadmium yellows, including Cadmium Yellow Lemon No.1, produced by the Parisian manufacturer Lucien Lefebvre-Foinet, considered to be “very high quality”.

In 2020, Mar Gómez Lóbon, an art curator based in Mallorca (Spain), studied the paints used by Miró after he settled on the island in the 1950s. A conservator from the Pilar and Joan Miró Foundation had him reported that more than 25 pieces in the foundation’s collection, painted in the 1970s, showed signs of yellow deterioration.

To identify the cause of this phenomenon and whether it was linked to a particular brand of paint, Mar Gómez Lóbon and his colleagues took microscopic samples of cadmium yellow paint from three untitled pieces that Miró created between 1973 and 1978. The team also collected paint fragments from three tubes of paint from the artist’s Taller Sert and Son Boter workshops, a cup used for mixing paint and two palettes. Each sample measured approximately one millimeter.

The scientists analyzed the nine samples of the paints and materials by measuring their interactions with different wavelengths of light. This allowed them to examine the chemical composition and crystal structure of each sample.

Analyzes revealed that the samples of the three degraded paints all contained mainly cadmium and sulfur, as expected, with traces of zinc. The same composition was found in the paint samples from the two palettes and one of the paint tubes, the Cadmium Yellow Lemon No.1. These six samples all had low crystallinity, meaning the cadmium and sulfur atoms were poorly arranged. This low crystallinity makes the pigment more susceptible to oxidation by air, which causes a loss of color and luster, degrading the works.

Mar Gómez Lóbon plans to inventory the hundreds of tubes of paint that are still in Miró’s workshops. She wants to establish the exact date of the Lucien Lefebvre-Foinet tubes and analyze the manufacturing of their paint, in particular cadmium yellow.

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